The present invention relates generally to the testing of semiconductor devices and in particular to the fabrication of a micro-cantilever style contact pin structure as probe card for the test of microelectronic devices.
When electronic devices such as semiconductor integrated circuits, LCD, PDP, FPD are produced they are inspected prior to being shipped out to verify their electrical characteristics as designed. A probe station, schematically shown in FIG. 5A, is commonly urged for such inspection. The probe station includes a probe card with a plurality of probes that couple test signal generation/detection circuitry of the probe station to one or plurality of pad(s) on a device undergoing inspection. The probe card is divided largely into two parts, i.e., a printed circuit board 12 and a plurality of probe needles 13 (xe2x80x9cprobesxe2x80x9d hereafter). The circuit board 12 structurally supports the probes 13 and has wiring such that test signals from the signal generation/detection means can be communicated all the way to the pointed tips of the probes 13. The probes are made to contact respective pads on the device 6 during inspection, as shown in FIG. 5A.
The probe card is attached to the lower side of an insert ring which is connected to a head plate 10 in the periphery of the probe station. An electronic device 6 to be tested is placed on a stage 14, which is positioned below the probe card and is controlled to move horizontally and/or vertically in order to align with the probe card above. The probe station generates electric signals and transfers the signals to the probe card via so-called pogo pin 11 before applying them to electrical contact pads 5 (See FIG. 5B) of the device 6 via wiring formed on the probe card in order to see if the device works as designed. Signals from the device 6 are transferred to the probe station via the same path.
The conventional structure shown in FIGS. 5A and 5B is called as the horizontal type or the tungsten needle type. In this conventional structure, a tungsten needle 13 having the sharpened end portion is fixed to the station, and the sharpened end portion contacts the pad 5 of the device 6 to measure the electrical characteristics of the device. However, as the semiconductor device become smaller, the pads also becomes smaller, with side of several tens micrometers and with several tens of micrometers spacing. The width of the tungsten needle used in the conventional type is in the range of several hundreds micrometers, and therefore it is impossible to contact adjacent pads or to measure all circuit patterns which are needed to verify the circuit characteristics. Furthermore, it is difficult to assemble the probe needles accurately at desired positions since the tungsten needles are fixed on probe card manually under microscope.
To overcome the above-mentioned problems, micromachining has been adopted for the fabrication of the probe portion. Some representative of macromachined probes are disclosed in the U.S. Pat. Nos. 4,961,052, 5,172,050, 5,723,347 and 5,869,974. Micromachining technology has been extensively developed for fabrication of mechanical structures sized less than millimeter down to few microns. Further, micromachining usually employs photolithographic process which ensures accurate positioning of the structure. Application of micromachining allowed fabrication of smaller probes disposed on the substrate, and a large number of probes can be arranged with narrow spacing. Further, the electrical characteristics of the probe card are improved since the probes are very short. Further, micromachining process using silicon as the base material hag been well established. Silicon, especially in single crystal form, has excellent elastic property which can be readily used for probe structure material. It is important that all the probes can accurately contact the pads of the device, and therefore, each of the probes should contact the pad by pressing with a predetermined value of pressure to ensure the accurate contact between the probe and the pad, and the sharpened end portions of probes should be placed at uniform height to maintain the preferred co-planarity. If the probe has elasticity and can be elastically deformed, the desired measurement can be accomplished even when the sharpened end portions of the probes are variously disposed or when the height of the pads varies, i.e., the semiconductor wafer, in which the device is located, is distorted. Therefore, the probe is required to have elasticity. Employing elastic material such as silicon for the probe material can facilitate fabrication of elastic probes.
Silicon probes can be formed as membrane type probe card. However, membrane type probe card has disadvantage of small elasticity. This property is caused by the fact that the sharpened end portion of the probe is connected to the substrate in all 360 degree directions. To create probe card for large area probing, it is usually required elastic deformation of more than tens of microns and spacing between the centers of the sharpened end portions less than one hundred microns in some places. Membrane type probe meets the spacing requirement but usually it is not possible to satisfy the elastic deformation criteria.
Cantilever style silicon probes can overcome the disadvantage of membrane type card, provided that there is some space where the cantilever can be extended. The spacing between the centers of the sharpened end portions can be less than 50 microns. The disadvantage of silicon probe is the brittleness of silicon. Hence, to ensure sufficient elastic deformation, the length of cantilever should be lengthened accordingly. Further, the previous design of silicon cantilever usually employed stacking of multiple layers by various deposition methods, which complicates the fabrication process and also reduces the mechanical stability.
In view of the aforementioned problems for micromachined probes, it is an objective of the present invention to provide a probe card with improved mechanical property and relative freedom of size and position using silicon cantilevers for the testing of the microelectronic devices.
An objective of the present invention is to provide a micro cantilever-type probe disposed on a probe card, having such appropriate elasticity and mechanical strength that the probe would recover its unforced shape after deformation during an inspection and maintain its original shape even after three hundred thousand uses.
For this purpose, the present invention provides a probe card comprising an electrically insulated substrate fixed on a circuit board; a plurality of elastic probes with a sharpened end fixed on said insulated substrate; and wiring formed on said probe, said insulated substrate and said circuit board. The inventive probe is manufactured by patterning a substrate using photolithography and etching a portion except a pattern-defined portion. The insulated substrate controls the probe so that a deformation of said probe may be stopped before said probe reaches a limit of elastic deformation. The probe is coated by metal layer(s)
Further, according to the present invention, the probe card comprises a substrate made of insulating material and probes are made of single crystal silicon. That is, the probe, which comprises a base, a cantilever, and a pointed end, is made up of a single material. There is provided space between the substrate and the probes to allow the body of the probes to elastically move.